Flatten and compact *streamables arguments

Closes [#614][]

When broadcasting, ignore `""` and `nil` values, especially when they
are the only values when generating the streamable channel name and
content.

[#614]: #614

app/channels/turbo/streams/broadcasts.rb

@@ -75,8 +75,13 @@ def broadcast_refresh_later_to(*streamables, request_id: Turbo.current_request_i
   end
 
   def broadcast_action_later_to(*streamables, action:, target: nil, targets: nil, attributes: {}, **rendering)
-    Turbo::Streams::ActionBroadcastJob.perform_later \
-      stream_name_from(streamables), action: action, target: target, targets: targets, attributes: attributes, **rendering
+    streamables.flatten!
+    streamables.compact_blank!
+
+    if streamables.present?
+      Turbo::Streams::ActionBroadcastJob.perform_later \
+        stream_name_from(streamables), action: action, target: target, targets: targets, attributes: attributes, **rendering
+    end
   end
 
   def broadcast_render_to(*streamables, **rendering)
@@ -88,7 +93,12 @@ def broadcast_render_later_to(*streamables, **rendering)
   end
 
   def broadcast_stream_to(*streamables, content:)
-    ActionCable.server.broadcast stream_name_from(streamables), content
+    streamables.flatten!
+    streamables.compact_blank!
+
+    if streamables.present?
+      ActionCable.server.broadcast stream_name_from(streamables), content
+    end
   end
 
   def refresh_debouncer_for(*streamables, request_id: nil) # :nodoc:

test/streams/broadcastable_test.rb

@@ -1,11 +1,30 @@
 require "test_helper"
 require "action_cable"
+require "minitest/mock"
 
 class Turbo::BroadcastableTest < ActionCable::Channel::TestCase
   include ActiveJob::TestHelper, Turbo::Streams::ActionHelper
 
   setup { @message = Message.new(id: 1, content: "Hello!") }
 
+  test "broadcasting ignores blank streamables" do
+    ActionCable.server.stub :broadcast, proc { flunk "expected no broadcasts" } do
+      @message.broadcast_remove_to nil
+      @message.broadcast_remove_to [nil]
+      @message.broadcast_remove_to ""
+      @message.broadcast_remove_to [""]
+    end
+  end
+
+  test "broadcasting later ignores blank streamables" do
+    assert_no_enqueued_jobs do
+      @message.broadcast_append_later_to nil
+      @message.broadcast_append_later_to [nil]
+      @message.broadcast_append_later_to ""
+      @message.broadcast_append_later_to [""]
+    end
+  end
+
   test "broadcasting remove to stream now" do
     assert_broadcast_on "stream", turbo_stream_action_tag("remove", target: "message_1") do
       @message.broadcast_remove_to "stream"